1. Field of the Invention
This invention relates to cables for a variety of electrical ignition systems. Specifically, it relates to improved electrical-pulse-carrying cables having electromagnetic-radiation-suppression characteristics which can be efficiently manufactured using conventional techniques, are failure resistant and otherwise have enhanced operating characteristics. While the present invention will be described primarily in connection with its applicability to automotive ignition systems, it is not limited thereto as those skilled in the art will readily recognize.
2. Discussion of the Prior Art
Electrical cables for carrying pulsating currents must meet a number of requirements, sometimes conflicting, including the reliable delivery of the electrical pulse from where it is generated, e.g., the ignition coil of a car, to where it is employed, e.g., the spark plug of an internal combustion engine. As has been long recognized, however, the electromagnetic field generated by the electrical pulses must be suppressed so as not to interfere with other commonly encountered electronic devices, including, for example, radio and telephone communication systems, but particularly on-board automotive devices.
Prior-art electromagnetic suppression cables have successfully coped with the electromagnetic radiation problem but occasional breaks in the lengthy spirally-wound metal conductors employed in many of such cables due to deterioration, fatigue, vibration, mechanical stress or the like may lead to cable failure or unshielded sparking or both. Thus, a cable may fail to perform its basic function of conducting the electrical pulse, or such conduction may be accompanied by unacceptable electromagnetic interference. In the case of an automotive ignition cable, a break in the wire may result in the failure of the spark plug to fire, rendering the associated cylinder inoperative, or unsuppressed sparking, resulting in undesired interference, as those skilled in the art are fully aware.
Periodic routine checking of prior art ignition cables having suppression characteristics will not necessarily reveal a potential for incipient wire failure. As a result, in the case of motor vehicles, the first sign of wire failure may be cylinder-firing disruption or failure or excessive electromagnetic interference. Such failures may occur at inconvenient times or inconvenient locations, resulting in unscheduled costly and untimely maintenance requirements.